1. Field of the Invention
This invention concerns an improved process for preparing acetic and propionic acids and their esters by a single stage reaction of oxides of carbon with hydrogen in presence of a catalyst system.
2. Prior Art
There are ever-increasing efforts to provide new methods of making carboxylic acids such as acetic acid and esters thereof which are particularly useful in preparing a wide variety of organic compounds such as cellulose acetate, vinyl acetate etc. An ever present aim is to prepare such material in relatively high yields directly from carbon monoxide and hydrogen utilizing a catalyst system providing good selectivity.
A number of processes have been described in the literature for manufacturing carboxylic acids and esters from carbon monoxide and alcohols or from carbon monoxide and hydrogen. For example, in U.S. Pat. No. 3,717,670 a method for preparing such carboxylic acids is disclosed in which an alcohol and carbon monoxide are reacted in the presence of a catalyst composition consisting of a rhodium compound and, for example, chromium trioxide. When hydrogen and carbon monoxide are passed over a catalyst comprising rhodium in combination with molybdenum and/or tungsten a reaction product containing acetic acid, acetaldehyde and/or ethanol is formed according to the disclosure of U.S. Pat. No. 4,096,164. A similar method is described in U.S. Pat. No. 4,014,913 where carbon monoxide and hydrogen are reacted in the presence of a rhodium-manganese catalyst. The reaction of carbon monoxide and hydrogen in the presence of rhodium metal catalyst to give a liquid product containing a substantial proportion of acetic acid, ethanol and/or acetaldehyde is disclosed in U.S. Pat. No. 4,246,186. Likewise in U.S. Pat. No. 4,162,262 it is noted that the reaction of hydrogen and carbon monoxide in the presence of a catalyst comprising thorium and/or uranium yields a product containing a large amount of two-carbon atom products. Other processes for preparing carboxylic acids from carbon monoxide and hydrogen are disclosed in U.S. Pat. No. 4,101,450 and in Dutch Pat. Nos. 7,500,910 and 7,500,918.
One serious problem associated with synthesis gas operations in the past has been the non-selectivity of the product distribution since high activity catalysts generally yield a liquid product containing numerous hydrocarbon products and hydrocarbons as well. Thus, complicated recovery schemes are necessary to separate the desired products and the overall yield of the valuable organic products is low. This is a definite need in the art for a process which will produce acetic and propionic acids and their esters in high yield and which does not require the use of an iodine-containing promoter.
This invention therefore is to provide a process of making acetic and propionic acids and esters thereof by resort to a unique bimetallic `melt` catalyst system which produces said acids and esters in good yields and with excellent selectivity.